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LMH6526: Question Regarding Stability of LMH6526

Zhaoqiang Peng
Prodigy 30 points
Part Number: LMH6526

Hi,

I tried to use LMH6526 to drive a SOA. It's acceptable although there were some overshot at 10ns pulse. But when a ~700Hz fluctuation showed my optical output intensity, I felt hopeless. Is there any data can tell me the stability of this chip like output pulse current verse time? And by the way, do you think a 40mA example in datasheet is able to tell the performance of a 600mA chip?

Best,

ZQ

  • 0
    TI__Mastermind 23106 points
    Hi ZQ,

    Can you provide the circuit that you are using, especially the amplifier's load? The stability is not technically related to the pulse width, and we can be compensate based on your circuit. You can only get 600mA from summing all the channels together, so yes the 40mA example is not demonstrating this.

    Best regards,

    Sean
  • 0 in reply to Sean Cashin
    Prodigy 30 points

    Hi Sean,

    Thanks for your reply. I don't know the load of SOA since there's nothing at its website. But I'm contacting the manufacturer to request the information. Meanwhile, I tried to connect 5 Ohm as load, used 300mA output channel, and set pulse width as 20ns. The pulse is around 1.5V which is correct for 300mA. However, the overshot approximate 2.8V, and some ripples at pulse certainly decrease the laser's performance. Could you give me any suggestion on dealing with this unexpected pulse shape?

     

    Best,

    ZQ

  • 0 in reply to Zhaoqiang Peng
    TI__Mastermind 23106 points
    Something is definitely wrong. Can you please show us your circuit. What are your Rf and Ra values? What are you using to drive your input current signal?
  • 0 in reply to Sean Cashin
    Prodigy 30 points

    Please check the circuit below. I only used channel 2 to send a differential pulse signal in and turned off internal oscillator by connecting to ground.

  • 0 in reply to Zhaoqiang Peng
    TI__Mastermind 23106 points
    Hi ZQ,

    How are you injecting the input current? All I can see is a switch to ground connected to I2 through a variable resistor and a 1k resistor? Typically this function is done with a current output DAC.

    Best regards,

    Sean